Traditionally, the thermal conductive materials used in heat generating electronic components to help dissipate heat can be divided into the following types:
The first type is a thermal conductive ceramic material, which uses ceramic thin plate as thermal conductive pad. It is mainly mica and graphite. When in use, both sides of the thermal conductive plate should be applied with thermal conductive paste to reduce interface resistance. But the disadvantage is that it is easy to break and hard to cut.
The second type is a thermal conductive pad, which uses thermal conductive polymer to apply on glass fiber fabric. The advantages for glass fiber fabric are high tensile strength and flexibility, cuttability and toughness. The disadvantages are thickness over 0.05 mm and unlikely below 0.1 mm with coated polymer. Thus, its thermal resistance is high and finds application in low heat generating components.
The third type is a thermal conductive paste, which is in a form of liquid or semi-solid thermal conductive paste that is formed of a liquid polymer and added ceramic powder, graphite or metal powder. This type of material has advantages of low thermal resistance and good thermal conductivity, but disadvantages of easy contaminating electronic components or circuit board, and besides, possibility of drying up and small molecule volatiles at high temperature.
The fourth type is a low melting point metal thermal conductive plate, which is a thermal conductive material made by applying alloy with melting point below 100° C. to both sides of metal foil. Because low melting point alloy has much less strength and ductility than normal metals, it can only be shaped when it is coated on metal foil. Such a material has disadvantages that alloy adherence diminishes when it melts, alloy leaks out under compression. As a result, performance will deteriorate. Furthermore, it does not provide stable quality and repeatable use.
Therefore, to overcome the above disadvantages, the industry has an invention of low softening temperature thermal conductive adhesive material. For example, the technology can be found in U.S. Pat. No. 5,950,066 and U.S. Pat. No. 6,197,859. The two patents disclosed the method to synthesize low softening temperature adhesive with C16 to C19 alkenes and C30 to C45 silanes and silicones with at least one hydrogen atom attached to one silicon atom. Then, a softening agent like vinyl acetate resin in 15˜20 weight units is added to increase flexibility. Thus, a low temperature thermal conductive material is made. However, because this process needs to use softening agent in the formulation, it takes longer time for the additional step. Besides, due to large difference in solubility parameter between different materials, phase separation occurs. Practically, the method disclosed in the patents is not a suitable process.